A particular problem in the recording of live information, i.e., the recording of events as they actually happen, is that a particular event of interest might occur without being recorded. For example, in videography, a videographer might monitor a location, such as a courthouse door, with hopes of capturing an event, such as the exit of a particular person. There are two primary reasons why such an event might not be captured by the videographer. First, the videographer might not start recording in time to capture the event. Second, the videographer might be recording, but might have to stop recording if no more media is available and a change to new media is not completed before the event occurs.
One mechanism has been suggested to solve this problem, and is illustrated in PCT Publication No. WO 96/26600. This publication describes a motion video camera which records video and audio media temporarily in a ring buffer. The data is written continuously to the ring buffer, and the ring buffer contents are overwritten, until the camera is triggered to end looped recording. The contents of the ring buffer are appended to a file which is subsequently recorded in a normal, linear recording mode. A form of buffer also is used in fault detection systems such as flight data recorders, shown in U.S. Pat. Nos. 4,409,670 and 5,056,056, and 4,646,241, and logic analyzers, shown in U.S. Pat. Nos. 4,373,193 and 4,139,903.
Maintaining data in a buffer and saving this data when a particular event occurs has several problems. First of all, a typical buffer is usually implemented in integrated circuit memory and thus usually holds only a few megabytes of data. Such a small buffer is insufficient for use in recording asynchronous motion video events. Second, using such a buffer requires an application to control the use of the buffer and the relationship of the data to any subsequently recorded data.